linux-kernel - Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS

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Message-ID: <20180805231544.GA209075@rodete-desktop-imager.corp.google.com>
Date:   Mon, 6 Aug 2018 08:15:44 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tino Lehnig <tino.lehnig@...tabo.de>, stable@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback
 feature

Hi Andrew,

On Fri, Aug 03, 2018 at 04:28:18PM -0700, Andrew Morton wrote:
> On Fri, 3 Aug 2018 11:51:43 +0900 Minchan Kim <minchan@...nel.org> wrote:
> 
> > > Is it legitimate to be altering the bdi capabilities at this level?  Or
> > > is this hacky?
> > 
> > Most of device's bdi capability seems to be static but there are few drivers
> > which can change capability. For example, BDI_CAP_STABLE_WRITES
> > 
> > drivers/scsi/iscsi_tcp.c
> > drivers/md/raid5.c
> > 
> > I believe it's driver itself advertisement stuff so I hope it's not hack.
> 
> The bdi is per-disk (per-queue).  So if zram changes the bdi for a
> particular partition then it is accidentally mucking with the other
> partitions as well, and it shouldn't do that.  At least, I think that's

Aha, I didn't know that. Thanks for the heads up.
However, I think zram doesn't support partitioning due to lacking of
probe feature via blk_register_region. ;-)